How to change material properties with time
First you have to set everything up and then click "I" on the color bar.
Next You have to go to the desired time where the colour change will end on the timeline. After that change the colour of the Halo. Finally click "I" on the colour bar again. This sets the selected colour to the selected time on the timeline.

Final Product:

NOTE: Example above is made in Blender Render since it takes a long time for a cycles animation, but this also works in Cycles as well.

BTW This is probably not the kind of "Halo" you are talking about, but it's a good example.